1. Field of the Invention
The invention relates generally to electric power distribution systems and, more particularly, to electrical enclosure assemblies for switchgear employed in such electric power distribution systems. The invention also relates to electrical enclosure assemblies for venting of gasses due to electrical arcing.
2. Background Information
Switchgear for electric power distribution systems includes electrical switching apparatus and their line and load terminations together with related equipment mounted in an electrical enclosure (typically a metal cabinet). Switchgear used in sections of electric power distribution systems operating at voltages up through 690 volts is classified as low voltage switchgear (according to international standards, although the ANSI standard for low voltage is a maximum of 600 volts). Typically, the electrical switching apparatus is a circuit breaker, but other switching apparatus such as, for example, network protectors, disconnect switches, and transfer switches are also mounted in such electrical enclosures. Henceforth, the electrical switching apparatus will generally be referred to as circuit breakers, although it will be understood that other types of electrical switching apparatus can be used as well.
Typically, in such low voltage switchgear, multiple circuit breakers are mounted in each cabinet in cells stacked vertically in a forward compartment. The line and load conductors are mounted in rearward compartments and engage the circuit breakers through quick disconnects as the circuit breakers are installed in the cells.
Some electrical switching apparatus can be relatively large. In order to facilitate movement (e.g., installation; removal; maintenance), some circuit breakers are commonly coupled to draw-out mechanisms which permit such circuit breakers to be drawn out of the electrical enclosure. Accordingly, such circuit breakers are commonly known in the art as “draw-out” circuit breakers. Draw-out circuit breakers are described in further detail, for example, in commonly assigned U.S. Pat. No. 7,019,229, which is hereby incorporated herein by reference. See also U.S. Pat. Nos. 4,002,864; 4,002,865; 4,017,698; 4,728,757; 6,031,192; and 6,563,062.
The electrical enclosure for draw-out circuit breakers generally includes an outer structure having a top, a bottom, rear and side walls, and a front access door or easily removable panel.
Circuit breakers are designed to trip in response to a trip condition (e.g., without limitation, an overcurrent condition; an overload condition; a relatively high level short circuit or fault condition). A high current fault interruption, for example, typically results in a substantial arc in the arc chamber of the circuit breaker. The arc forms rapidly expanding gases and may also generate flames. The gases can be extremely hot, are at least partly ionized, and may carry debris, such as molten metal particles and fragments of various circuit breaker components. Furthermore, the gases and debris can be electrically conductive and, therefore, can cause additional undesirable arcing between the circuit breaker and grounded electrically conductive features proximate the circuit breaker, including but not limited to, the metallic enclosure in which such circuit breakers are typically installed. The gases may also be expelled with explosive force and may, therefore, damage components of the enclosure. Expelled gases may also pose a risk to an operator performing normal operating duties in close proximity to such equipment operating under normal circumstances.
Similar arcing can occur between adjacent conductors of different potentials, between an outboard line or load conductor and the switchgear cabinetry, and between the quick disconnects that are electrically connected with the line and load conductors. Such arcing events are generally of greater magnitude and duration than those produced from fault interruption due to tripping of a circuit breaker. Such potential arcing events could result from a number of different scenarios such as, but not limited to: an operator leaving a tool in the switchgear prior to energizing the switchgear, an operator leaving a tool (or other object) on the back of a circuit breaker while racking the breaker onto a live bus, buildup of debris within the switchgear, animals entering the switchgear through venting holes and crossing a live bus, or some other type of unforeseen failure within the switchgear. Severe injury/damage can occur to an operator or other person(s) and equipment nearby if the electrical enclosure is not designed to manage and vent in a controlled manner the large volumes of gas and debris formed from such an arcing event. While known enclosure designs provide vents through which arc gases may pass, such vents are typically designed primarily for cooling of the interior of the enclosure and as such do not provide much, if any, control over potential arc gas venting, particularly not of large scale arc gas formations. Additionally, such vents do not provide for control over debris produced by arcing events which can contaminate other parts within the enclosure which may lead to other arcing events among other detrimental effects.
There is, therefore, room for improvement in electrical enclosures and systems used therein to manage large scale arcing events and particularly the large volumes of gas formed as a result of such arcing events.